In my patents 4,957,429, and 5,085,581 there are disclosed method and apparatus for removing volatilizable organic materials from particulate mineral compositions. The aforesaid process and apparatus are generally quite suitable for treating particulate compositions in which the amount of fine particles are below about 25% of the total recoverable mass of material. In the process, fine particles are separated from a gaseous mixture recovered from the heating drum, and returned to the drum and further heated along with the coarse particles for removal of volatilizable organic material. It has been found that in treating contaminated soil compositions, where the amount of fine particles which pass a size 40 U.S. series sieve is substantial, the continuous return of fines to the heating drum reduces production efficiency. The efficiency drop becomes especially problematic where the amount of fines is over about 50% of the recoverable soil composition mass, and where the fines present are above about 60% or 70%, production efficiency drops dramatically. It is to an apparatus and process for treating contaminated soils which are relatively high in fine soil particulates that the present invention is directed.